#define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<vector>
#include<queue>
using namespace std;
const int maxn = 2e5;
double p[1005], dp[1005],q[1005];
int n;
double v(int x){
	return p[x] * (1 - dp[x]) * q[x];
}
int main(){
	cin >> n;
	for (int i = 0; i < n; i++){
		scanf("%lf", &p[i]);
		p[i] /= 1e3;
	}
	for (int i = 0; i < n; i++){
		scanf("%lf", &q[i]);
		q[i] /= 1e2;
	}
	double g = 0;
	for (int i = 1; i < maxn; i++){
		int x = 0;
		for (int j = 0; j < n; j++){
			if (v(x) < v(j)) x = j;
		}
		g += i * v(x);
		dp[x] += (1 - dp[x]) * q[x];
	}
	printf("%.7lf\n", g);
	return 0;
}